[Dave I.]

Well first post for the chassis section...

How much does it help the launch / 60' times when someone adds 1,2,3 inches to the wheelbase by having it built into the a-arms? I have wondered for a while. I realize it changes instant center of the bike, but what else is to be gained?

Is there any rule of thumb to say if you add an inch to the front you can remove an inch from the swingarm / rear etc?

 

[Ziggy]

I have found with most chassis designs the wider you go it is just adding weight. Now with that said there is something to be said about keeping the chassis rideable. so when you narrow the rear axle on a 300 ft sand bike your times will improve. but at to what ratio?.. I guess that depends on how brave you are, most riders lean to steer as the front tires should be off the ground for at least half the track, so in that case when you narrow the rear of the bike you can only lean a small amount to make adjustments. when a new rider throws a leg over a really narrow bike for the first time they end up all over track becasue they are over compensating. with a wider front end the rider can let off and the bike will correct it self a little. warning* haveing the front end too wide can cause the bike to want to "come around" or go sideways under heavy braking. I know some of you have had this happen becasue you see it all the time in the dunes. the front end is wider in than the rear by allot and this causes the rear to move sideways under heavy brakin. when it does this the rider leans making the rear shoot to the other direction. it is very dangerous having a front end that is anything over 3 inches wider than the rear in drag racing. But making the rear narrow will help ET. so the rationship all depends on the rider and the chassis design the longer the bike is the closer the realtionship has to be. the shorter it is the more leway you have.

This probably just confused the question.. Just my 2 cents.

 

[Dave I.]

Thanks for that info Ziggy. Good to know as well.

I was originally thinking more along the lines of the arms that move the ball joints or heim joints forward on the arms to gain wheel base.....Like the metal tech drag arms.

Like these. +0 width +3.5 forward

 

[phatboyz]

depends on how wide the back is as to how far you go wider on the front.

 

[Ziggy]

Got ya, i would never remove from the swingarm what i added to the front. most drag bikes have to have a min of +10 in the rear and anything you put in front is just going to make the transfer better. your instant center of gravity is the most important thing on the launch. the lower the bike is and the longer it is are both huge factors on how it hooks up. If you want to add front end. it will help get more weight to the rear when the front end is over the instant center. but you must make sure your instant center is low enough for this to work out. there are some good program and excell spreadsheets for this. I will try to dig some up.


Ziggy

 

[BBIII]

Ok i have a question.

How would you decide if you set your front end out there far enough?

I am thinking of making some arm's and exteneding the front end of the bike but not sure on how far to go.
My motor right now is a 350 but i plan on building a bigger motor this winter for it.

 

[Ziggy]

i dont think it's a question of far enough.. more like how far can you go and maintain the steering geometry. if your using a stock frame. you really can't go more than 3 inches safely and that may take a steering stem modification to be safe. the stock banshee frame has terrible steering geometry already and if you do go forward without moving the stem your asking for problems. i have done a couple sets of forward arms and they really need longer arms that attach to the spindles, then you need to modify the steering stops so your wheel does turn in and get stuck.

 

[Fouledout421]

Good thread Dave!

 

[BBIII]

I have no problem moving the steering up if i need to cause i need it to be safe.

Just wondering on how far forward i should go on it.

It will be a dune and track racer.

 

[phatboyz]

ya but untill you move the position of the motor in the frame forward as well with the center the extension of the frame is kinda useless aint it?

 

[Dave I.]

QUOTE (phatboyz @ Jun 8 2008, 07:19 PM) index.php?act=findpost&pid=2225ya but untill you move the position of the motor in the frame forward as well with the center the extension of the frame is kinda useless aint it?


No, Not really. Im going to do a horrible job of explaining it but ill try to make sense.......there is an imaginary line that runs from the rear axle to point on the bike that is basically like a point of leverage...where the rotational twist of the tires transfers into the lift/leverage to pick up the front end and plant the tires......I have no idea where that line is on a banshee.....there are programs like Ziggy talked about where you can input information about your chassis, wheelbase etc and find the instant center......moving the instant center location around will change how the bike launches and works.....

Like I said, hardly a good explanation.......ive seen it done on race cars but a banshee is a new world for me really.

 

[Ziggy]

QUOTE (Dave I. @ Jun 8 2008, 08:31 PM) index.php?act=findpost&pid=2235No, Not really. Im going to do a horrible job of explaining it but ill try to make sense.......there is an imaginary line that runs from the rear axle to point on the bike that is basically like a point of leverage...where the rotational twist of the tires transfers into the lift/leverage to pick up the front end and plant the tires......I have no idea where that line is on a banshee.....there are programs like Ziggy talked about where you can input information about your chassis, wheelbase etc and find the instant center......moving the instant center location around will change how the bike launches and works.....

Like I said, hardly a good explanation.......ive seen it done on race cars but a banshee is a new world for me really.

suspended chassis are extremely hard to figure out. but if you have struts with the right program its pretty easy. good Explanation Dave. right on!

 

[Fouledout421]

QUOTE (Dave I. @ Jun 8 2008, 11:31 PM) index.php?act=findpost&pid=2235No, Not really. Im going to do a horrible job of explaining it but ill try to make sense.......there is an imaginary line that runs from the rear axle to point on the bike that is basically like a point of leverage...where the rotational twist of the tires transfers into the lift/leverage to pick up the front end and plant the tires......I have no idea where that line is on a banshee.....there are programs like Ziggy talked about where you can input information about your chassis, wheelbase etc and find the instant center......moving the instant center location around will change how the bike launches and works.....

Like I said, hardly a good explanation.......ive seen it done on race cars but a banshee is a new world for me really.

You explained it a heck of a lot better then I was going too! lol

 

[BLK]

QUOTE (Dave I. @ Jun 8 2008, 08:31 PM) index.php?act=findpost&pid=2235No, Not really. Im going to do a horrible job of explaining it but ill try to make sense.......there is an imaginary line that runs from the rear axle to point on the bike that is basically like a point of leverage...where the rotational twist of the tires transfers into the lift/leverage to pick up the front end and plant the tires......I have no idea where that line is on a banshee.....there are programs like Ziggy talked about where you can input information about your chassis, wheelbase etc and find the instant center......moving the instant center location around will change how the bike launches and works.....

Like I said, hardly a good explanation.......ive seen it done on race cars but a banshee is a new world for me really.

Pretty good explanation! If you guys do a little research into asphalt drag race suspension tuning it will deal with the instant center and center of gravity. There are many ways to tune a chassis and I'm suprised no one is making a 4-link suspension work on a quad. Bryan

 

[okbeast]

QUOTE (1700camaro @ Jun 9 2008, 08:26 AM) index.php?act=findpost&pid=2248Pretty good explanation! If you guys do a little research into asphalt drag race suspension tuning it will deal with the instant center and center of gravity. There are many ways to tune a chassis and I'm suprised no one is making a 4-link suspension work on a quad. Bryan

Do you asphault guys run struts or some type of shock? 4-links are setup for using shocks correct, so the guys running struts wouldn't really benefit would they.

 

[BBIII]

I would think on a 4 link setup you would need a panhard bar back there to help keep everything center, wouldn't ya?

 

[BLK]

QUOTE (okbeast @ Jun 9 2008, 06:35 AM) index.php?act=findpost&pid=2250Do you asphault guys run struts or some type of shock? 4-links are setup for using shocks correct, so the guys running struts wouldn't really benefit would they.

We run a strut, but I don't think that's the best way to do it. I'll be testing a shock hopefully some time this year. I've been trying to work with AFCO for a fully adjustable shock for the quad.

Now this is only my opinion, but I think a 4-link could be used in a strut application. I don't think you could use the full benefits with out a shock. We have tested different angles of the swingarm with a strut and found it makes a difference.

 

[dajogejr]

Damn good thread and good reading...

 

[BBIII]

So on a stock frame should i just make the arm's forward and narrower then instead of messing with making the frame longer out front?

 

[GPracerX]

QUOTE (1700camaro @ Jun 9 2008, 10:38 AM) index.php?act=findpost&pid=2254We run a strut, but I don't think that's the best way to do it. I'll be testing a shock hopefully some time this year. I've been trying to work with AFCO for a fully adjustable shock for the quad.

Now this is only my opinion, but I think a 4-link could be used in a strut application. I don't think you could use the full benefits with out a shock. We have tested different angles of the swingarm with a strut and found it makes a difference.



Its simple if you run a strut on a 4 link you now negate the suspension all together and now have a ridged chassis
Zig actually a ridged is very simple.....
the instant center is at the rear tire contact patch!
or at least untill it hits the wheely bar

weight transfer is very simple to calculate if you know your acceleration..
http://www.dur.ac.uk/r.g.bower/PoM/pom/node16.html

I have a better formula i will look up for ya